Sustainability action at universities is complex and requires engaging multiple competences that reside on different levels outside and inside the organisation. In addition to individual competences, social communities also possess collective resources and characteristics that do not translate into a sum of individual abilities. Based on a qualitative small-n comparative study of four universities in Spain, Portugal, Finland and Romania, this paper explores the concept of collective sustainability competences as enablers and constraints of sustainability action at universities. Drawing from institutional theory and nestedness in organisations, the article poses the following research question: How can the collective sustainability competences of universities be conceptualised? The article develops a conceptual understanding of regulative, normative and cultural-cognitive elements of collective sustainability competences as a nested institutional space. In so doing, the article contributes to the discussion on the capacity of universities to act as key organisations in sustainability transitions.